Apply TypeVar defaults (functions)

Author: cdce8p

mypy/applytype.py

@@ -17,6 +17,7 @@
     TypeVarLikeType,
     TypeVarTupleType,
     TypeVarType,
+    UninhabitedType,
     UnpackType,
     get_proper_type,
 )
@@ -102,7 +103,9 @@ def apply_generic_arguments(
         target_type = get_target_type(
             tvar, type, callable, report_incompatible_typevar_value, context, skip_unsatisfied
         )
-        if target_type is not None:
+        if isinstance(target_type, UninhabitedType) and tvar.has_default():
+            id_to_type[tvar.id] = tvar.default
+        elif target_type is not None:
             id_to_type[tvar.id] = target_type
 
     param_spec = callable.param_spec()

test-data/unit/check-typevar-defaults.test

@@ -71,3 +71,27 @@ Ts1 = TypeVarTuple("Ts1", default=2)  # E: TypeVarTuple "default" must be a type
 Ts2 = TypeVarTuple("Ts2", default=int)  # E: The default argument to TypeVarTuple must be an Unpacked tuple
 Ts3 = TypeVarTuple("Ts3", default=Tuple[int])  # E: The default argument to TypeVarTuple must be an Unpacked tuple
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarDefaultsFunctions]
+from typing import TypeVar, ParamSpec, List, Union, Callable, Tuple
+from typing_extensions import TypeVarTuple, Unpack
+
+T1 = TypeVar("T1", default=str)
+P1 = ParamSpec("P1", default=(int, str))
+Ts1 = TypeVarTuple("Ts1", default=Unpack[Tuple[int, str]])
+
+def callback1(x: str) -> None: ...
+
+def func1(x: Union[int, T1]) -> List[T1]: ...
+reveal_type(func1(2))  # N: Revealed type is "builtins.list[builtins.str]"
+reveal_type(func1(2.1))  # N: Revealed type is "builtins.list[builtins.float]"
+
+def func2(x: Union[int, Callable[P1, None]]) -> Callable[P1, None]: ...
+
+reveal_type(func2(callback1))  # N: Revealed type is "def (x: builtins.str)"
+reveal_type(func2(2))  # N: Revealed type is "def (builtins.int, builtins.str)"
+
+def func3(x: Union[int, Callable[[Unpack[Ts1]], None]]) -> Tuple[Unpack[Ts1]]: ...
+# reveal_type(func3(callback1))  # Revealed type is "builtins.tuple[str]"  # TODO
+# reveal_type(func3(2))  # Revealed type is "builtins.tuple[builtins.int, builtins.str]"  # TODO
+[builtins fixtures/tuple.pyi]